The line-of-sight detection technology is a technology for specifying the place the observer observing the object is looking at and is used in various situations. For example, a screen of a personal computer (PC), a display shelf of a commodity at a store, or the like can be an observed object.
Related art is disclosed in International Publication Pamphlet No. WO 2009/019760, Japanese Laid-open Patent Publication No. 7-308290, or Gu Li Gang, Kazuyoshi Sakamoto, “Studies on the evaluation of Visual Fatigue in VDT work by involuntary eye movement (flick)”, Ergonomics, Vol. 32, No. 2, pp. 87-97, 1996.